a. Field of Invention
The invention relates generally to an interlocking mainframe rail and sash slot system, including an integrated interlocking mainframe rail and sash slot system for double hung windows that may be resistant to negative pressure wind load.
b. Description of Related Art
Conventional systems to achieve high resistance to negative pressure wind load may have a number of deficiencies. For example, in a conventional pocket sill design, a sash may be held structurally in place by sitting in a deep recessed pocket with the sill. The pocket sill design may increase the air infiltration rate of the window because of the requirement to weep water out of the pocket during rain or snow through exterior weep holes connected to the pocket. The pocket sill design may also collect and concentrate dirt in the pocket area, which may be visible when the sash is in the open position. In a conventional sill dam and header sash lift rail interlock, the sash member may be overlapped with sill and header dams. The header dams may be visible and must be machined off before exterior finishes, such as wood grain laminates, may be applied. Accordingly, the removal of the dams in order to finish the exterior of the windows may negate or eliminate the usefulness of the sill dam and header.
Some attempts have been made to utilize flange and groove designs to lock a window sill and sash together. However, these designs are disadvantageous because the flange is completely straight with a constant width along the entire height of the flange. The shape of the straight flange is not conducive to locking the sill and sash in engagement with each other (i.e., locking the straight flange of the sill within the groove of the sash).
Accordingly, there remains a need for system to lock a window mainframe and sash that minimizes and/or eliminates these deficiencies in the prior art.